You're trying to get libvirt and KVM working on Red Hat Enterprise Linux 6 or CentOS 6, or maybe even Scientific Linux 6. But it's not going well.
You wanted your VMs to have full access to the network and you've discovered that virbr0
doesn't do that. Finally you stumbled upon the way to do it by Creating a Network Bridge using your primary interface. And yet, something just ain't right.
You've verified that bridge-utils is in fact present:
# rpm -q bridge-utils
bridge-utils-1.2-9.el6.x86_64
Telltale signs are this message during network startup:
Device bridge0 does not seem to be present, delaying initialization.
And the following entries in /var/log/messages:
/sys/devices/virtual/net/bridge0: couldn't determine device driver; ignoring...
and
ifcfg-rh: parsing /etc/sysconfig/network-scripts/ifcfg-bridge0 ...
NetworkManager[1802]: ifcfg-rh: error: Bridge connections are not yet supported
You've stared at your /etc/sysconfig/network-scripts/ifcfg-bridge0 file until your eyes hurt, yet nothing seems to be wrong:
DEVICE="bridge0"
TYPE="bridge"
BOOTPROTO="none"
ONBOOT="yes"
IPADDR="203.0.113.2"
NETMASK="255.255.255.0"
DELAY=0
GATEWAY="203.0.113.254"
DNS1="x.x.x.x"
I'm here to tell you: you forgot to capitalize the word Bridge in your TYPE entry.
DEVICE="bridge0"
TYPE="Bridge"
BOOTPROTO="none"
ONBOOT="yes"
IPADDR="203.0.113.2"
NETMASK="255.255.255.0"
DELAY=0
GATEWAY="203.0.113.254"
DNS1="x.x.x.x"
Have a nice day!